Taxi
Williams, 1988When I turn my Taxi on for the first time after a few hours, a few specific segments on the main score display flicker for a few minutes before stabilizing. This isn't an issue with the other power supply I have, so I figure there's something going on with the original one.
I have the schematic in front of me, but I'm curious about what could cause the temporary flickering. That seems like something a less-than-awesome capacitor might cause. Does that sound right?
Just to clarify: the flickering does not occur with a replacement power supply?
If so, measure the hi voltage out of both boards. Is the one causing the flicker considerably less voltage at the output stage?
I just fixed a flickery Fire! pinball display by changing the display ribbon cable. Lightly corroded batteries had offgased and roached various components on the board. The ribbon cable pins are very thin and flaky. And it wouldn't flicker right away. It had to warm up for a bit first.
Quoted from GRUMPY:C1 or C3 may be drying up. Best to just rebuilt the power supply.
I would agree, but I rebuilt the power supply with stuff from GPE less than two years ago, and the machine's barely been played. Maybe I'll swap them in from the known good power supply and see what happens.
Quoted from UvulaBob:Maybe I'll swap
Now that you have an O scope, use it to check the caps from a cold start for a few minutes until they warm up. Check for AC noise on there output side.
The Taxi manual has two schematics for a power supply, so I'm using the one that most closely matches the two I'm working with, which is the one with a fuse at F2 (on page 67).
Now, I don't know enough to call the 100v display circuit "rectified", but it certainly seems to have quite a few didoes and transistors that seem to ensure the current flows in a specific direction.
The only difference between my board and the known-good board is the 220 uf caps (which are part of the kit sold by GPE, so I trust those specs) and the 93v Zener diodes that I'm using at Z2 and Z4 (also at GPE's recommendation). I replaced those two Zeners with the 100v versions he provides with the kit (in case of problems similar to mine) and so far, so good. I'll turn it on again in a few hours to see if the initial flicker goes away.
Quoted from KenLayton:Check resistors R1 and R4 (39k). When they start going off value, weird stuff happens.
You could say that for anything in this circuit, really. What role do those resistors play in this circuit?
Quoted from UvulaBob:You could say that for anything in this circuit, really. What role do those resistors play in this circuit?
When they start going off value (usually increased resistance or they go open circuit) the output voltage drops (low +100 or -100). If they are open circuit the voltage drops to nearly zero volts.
A weak +100 volts or -100 volts will cause the display to dim or take a while to warm up or not have all segments lit.
If either or both the +100 and -100 volts are missing, the display will appear dead.
Wanna join the discussion? Please sign in to reply to this topic.
Great to see you're enjoying Pinside! Did you know Pinside is able to run without any 3rd-party banners or ads, thanks to the support from our visitors? Please consider a donation to Pinside and get anext to your username to show for it! Or better yet, subscribe to Pinside+!
This page was printed from https://pinside.com/pinball/forum/topic/flickering-displays-on-first-power-up and we tried optimising it for printing. Some page elements may have been deliberately hidden.
Scan the QR code on the left to jump to the URL this document was printed from.
Revere, MA
